The present invention relates to an interlock apparatus of a transfer machine for transferring a substrate such as an LCD substrate (Liquid Crystal Device substrate) or a semiconductor wafer.
In processing the LCD substrate and the semiconductor wafer, a so-called lithographic process is carried out to form a resist pattern on the upper surface of the LCD substrate or the semiconductor wafer. The lithographic process further includes various processing steps such as substrate cleaning, resist coating on the substrate surface, resist exposure, and development.
These steps are performed in a process system in which process machines responsible for these processing steps are collected in one place. In such a process system, a substrate is taken out from a cassette (accommodating a predetermined number of substrates) and transferred one by one between process machines such as a cleaning machine, a resist coating machine, and a developing process machine. The substrate is transferred from a process machine to another process machine by use of a transfer machine provided in the process system. Such a transfer machine has an arm for transferring the substrate to each of process machines, a drive unit for driving the arm, and a control unit for controlling the movement of the control unit. The arm is moved along a transfer path by a moving unit under the control of the control unit. When the arm goes in and out of each of process machines, a substrate is transferred.
The drive unit of the transfer machine mentioned above usually employs a high-torque motor to transfer a large LCD substrate. Therefore, the control unit thereof usually employs an interlock mechanism to ensure the safety operation. The interlock mechanism is used for stopping the movement of the arm in case unusual movement takes place. The interlock mechanism recognizes the movement by quantitative changes in three parameters: movement speed (acceleration) of the arm, deviation of the arm from a predetermined movement position (deviation counter overflow), and power driving the arm (torque limit). The interlock mechanism is designed to stop the movement of the drive unit when any one of the acceleration and deviation counter overflow exceeds its own threshold.
On the other hand, to improve the throughput, the arm of the transfer machine is desirably moved at a speed as high as possible and with a movement power as large as possible. It is also desirable that the transfer machine is continuously operated without stopping the movement even if the movement position of the arm deviates from the predetermined position to some extent (greater than the degree of the teaching time). To attain these, individual thresholds are preferably set at values as large as possible.
In the aforementioned transfer machine, prior to the practical processing of the substrate performed by the process system, so-called teaching is usually performed. The teaching is performed with respect to each process machine to determine the target positions such as a stop position of the arm on a transfer path and an entering position of the arm, and usually performed by an operator while visually monitoring the movement of the arm. More specifically, the arm is manually moved to a predetermined position, followed by storing the position data in the control unit. When the operator performs the teaching, as is often case, he enters the process system. Therefore, the thresholds for the interlock mechanism are desirably set to values as small as possible to ensure the safety of the operator. In other words, if each of the threshold values is set as small as possible, the drive unit can be stopped immediately when any of unusual movements takes place, for example, when the acceleration of the arm exceed the predetermined value, or the deviation counter over flow exceeds a predetermined one, even slightly. Also, when the arm strikes an operator or an obstacle, a large torque is occurred. Therefore, to ensure the operator's safety, it is required to set the threshold values as small as possible.